This invention relates generally to the telephone art and more specifically to the art of automatic number identification of telephones.
It is well-known in the art to use telephones generating dual tone multi-frequency signals (dtmf) in combination with pulse-responsive switching equipment at a telephone central office. The apparatus which converts the multi-frequency tones generated by such telephones into corresponding pulses compatible with existing central office switching equipment is known as a tone-to-pulse converter. Several types of tone-to-pulse converters are currently used, among them the converters disclosed in U.S. Pat. No. 3,133,155 to Kuchas and U.S. Pat. No. 3,291,913 to Hanna et al. By using such tone-to-pulse converters, however, which operate to momentarily break the circuit connection between the tip and ring lines from the central office, and the tip and ring lines in the telephone, the prior art system used with dial telephones for automatic number identification (ANI) of telephones using two-party lines is rendered inoperative.
The ANI system operates to automatically identify which party on a two-party line is making a long distance (toll) call, and hence, which party should be charged for the call. Such a system is, of course, unnecessary for single party lines. The use of such a system eliminates the need for an operator to come on the line whenever a long distance call is made by one party on a two-party line.
In such a system used with dial telephones, one party on a two-party line will have a ground loop (e.g. an inductor or resistor connected to ground) connected to either the tip or ring line in his telephone. The ground loop causes an imbalance between the voltage present at the tip and ring lines, respectively, when a voltage is placed across them. When one party on the two-party line makes a long distance call, he can be distinguished by ANI equipment at the central office from the other party on the two-party line through detection of the voltage imbalance (or lack thereof) between the tip and ring lines, due to the presence (or absence) of the ground loop connected to one line of the telephone of the calling party. For instance, if the tip party telephone includes the ground loop, and a voltage imbalance is detected by the central office ANI equipment, the tip party is making a call, while a voltage balance indicates that the ring party is making the call. The detection of the voltage imbalance can only occur during the time in which the central office is directly connected to the calling party, i.e. during dialing and switching, and typically occurs between the dialing of the first and second digits by the calling party.
Tone-to-pulse converters, however, break the circuit between the telephone and the central office during "dialing" to convert tones generated by a multi-frequency signal telephone into corresponding pulses recognizable by central office switching equipment, and the loss of circuit continuity during this time prevents the establishment of a voltage imbalance on the portion of the tip and ring lines connected to the central office, and hence prevents identification of the calling party. Unless remedied, an operator would be required to come on the line each time one of the parties on a two-party line attempted to complete a long distance telephone call.
In view of the above, it is a general object of the present invention to overcome the disadvantages of the prior art.
It is another object of the present invention to provide automatic number identification of each party on a two-party line.
It is another object of the present invention to provide an identification forwarding circuit which makes existing ANI equipment compatible with telephones using tone-to-pulse converters.
It is another object of the present invention to provide such a circuit which may be located within a telephone.
It is a still further object of the present invention to provide such a circuit which is inexpensive to manufacture and easy to install.
It is yet another object of the present invention to provide such a circuit which detects the presence or absence of a ground connection on the tip and ring line pair portion connected between a telephone and a tone-to-pulse converter during tone-to-pulse conversion.
It is a still further object of the present invention to provide such a circuit which duplicates the presence or absence of a ground connection on the tip and ring line pair portion connected between a telephone and a tone-to-pulse converter during tone-to-pulse conversion with respect to the tip and ring line pair portion connected between the tone-to-pulse converter and a central office during tone-to-pulse conversion.